The majority of the upper bowl at the O.Co Coliseum is closed to fans, and the seats are covered with green tarps painted with the team name. The luxury boxes shown are not being used during the Oakland A's game against the Blue Jays in Oakland, Calif., Wednesday, May 9, 2012.

Photo: Sarah Rice, Special To The Chronicle

The majority of the upper bowl at the O.Co Coliseum is closed to...

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The majority of the upper bowl at the O.Co Coliseum has been closed to fans, and the seats are covered with green tarps painted with the team name. A security guard watches the game from the only open sections, above home plate, during the Oakland A's game against the Blue Jays in Oakland, Calif., Wednesday, May 9, 2012.

Photo: Sarah Rice, Special To The Chronicle

The majority of the upper bowl at the O.Co Coliseum has been closed...

Most teams try to sell as many tickets as they can, especially during the playoffs. The Oakland Athletics have a different philosophy.

A's management said Friday that it does not plan to sell 20,878 of O.co Coliseum's 55,945 seats next week for the A's division showdown with the Detroit Tigers. Those seats account for about 37 percent of the Coliseum's baseball seating capacity, and A's management has sealed them off with tarps since 2006 due to low attendance.

But now the Oakland A's are drawing sellout crowds. So many fans showed up for the last game of the season on Wednesday that A's management warned people to stay away because there were no tickets left.

Fans are demanding that the team remove the tarps to let more people in - some have started a petition via a website called Removethetarps.com. Many have pelted A's management with complaints.

On Friday, A's management explained to The Chronicle why they would not remove the tarps.

More intimate

A smaller crowd, A's managers said, would create a closer, more intimate environment for the American League Division Series.

"The fan experience is better without spreading fans out over more seats," A's executives wrote in an e-mail. "The energy in the park and the fan experience over the last week (when the seats were tarped) was incredible."

Since 2006, shortly after Lew Wolff bought the team, most of the third deck and the outfield stands known as Mount Davis have been covered with dark green tarps. The Raiders, who share the Coliseum with the A's, remove the tarps for their home games.

The A's rationale is that most games are far from sellouts, so they want fans to gather in the lower decks rather than scatter throughout the stadium.

"Here's a team that says they need to leave Oakland because there's no support. Yet here you have thousands of people who are begging to put money in the A's pockets, and they tell fans, 'Sorry, you have to watch it on TV,' " said Doug Boxer, a former Oakland planning commissioner and organizer of an A's fan group called Let's Go Oakland. "It doesn't make any sense." So far this year, the A's have sold out only seven of 79 games in the 35,067 seats in the non-tarp area.

A's fans already feel betrayed by Wolff, who's been trying for years to move the team. He's awaiting word from Major League Baseball on his request to move the A's to San Jose, saying his team cannot succeed in Oakland while sharing a stadium with the Raiders, and Oakland has no other suitable sites for a ballpark. The team has defied all odds and expectations, however. Despite having the lowest payroll in the American League, the team shocked the sports world and thrilled their fans by overcoming a 13-game deficit and clinching the American League West title after sweeping the Texas Rangers.

They open the division series Saturday in Detroit and return to Oakland on Tuesday for the best-of-five series. That game is sold out, as is Wednesday's, if it's played.

A's managers said they'll roll up the tarps only if the A's reach the World Series.

That's not good enough, said Oakland City Councilman and Coliseum Authority Co-Chairman Ignacio De La Fuente.

'Denying fans'

"Anyone in their right mind would open those seats," he said. Keeping the seats closed "is denying fans the chance to show their incredible support for the A's. I don't understand it."

Even seasoned sports marketing professionals were bewildered by Wolff's decision.

Longtime sports marketer Paul Siri of Redwood City, a former executive with IMG, said he'd never seen an owner say "no" to the chance to sell more tickets, hot dogs, beer, T-shirts and other merchandise at a high-profile game that's sure to sell out.

The move makes sense only if Wolff is trying to convince Major League Baseball he can't build a successful team in Oakland, Siri said.

"Looking at this from his point of view, this is the worst thing that could happen," Siri said. "His team wins, media exposure increases, the stadium sells out, and suddenly he loses his leverage to move. It kills his argument. ... I don't blame the fans for being upset."

Sara Somers, an Oakland resident who's with a group called Save Oakland Sports, was reluctant to criticize Wolff but said the players deserve a strong, boisterous crowd.

"Intimate is not what you want for a playoff game. You want noise. You want the crowd's energy to be contagious," she said. "Management needs to give the team the best home-field advantage they can."